DESCRIPTION Calcium ions within a neuron control properties such as gene expression, differentiation, and synaptic transmission. Uncontrolled calcium levels, however, can lead to cell death. Over-accumulation of calcium within neurons, for example, is a cause of brain damage after stroke. Neurons maintain an overall low concentration of intracellular calcium, but with discrete pools of concentrated calcium for signal transduction. This proposal focuses on mechanisms of release and uptake of calcium from intracellular stores. The subcellular locations of molecules and processes that control store calcium-levels--ryanodine and inositol triphosphate receptors, calcium ATPase pumps, and release-activated calcium transport (RACT)--will be studied. It will be determined if the different processes control spatially separate pools of intracellular calcium. RACT has recently been discovered in frog sympathetic neurons; mammalian neurons will be examined for existence of RACT. Calcium levels will be measured using calcium-sensitive fluorescent dyes with photometric recording and confocal imaging systems, including a video-rate visible/ultraviolet confocal microscope system for fast time resolution.